High pressure and high temperature reaction system

ABSTRACT

In a high pressure and high temperature reaction system suitable for oxidative waste treatment, particularly a reaction system for supercritical water oxidation (SCWO), a method is disclosed for injecting a first fluid of a first temperature at a first flow rate into a second fluid of a second temperature at a second flow rate, mixing the first and the second fluids within a mixing length ( 115, 215 ), and wherein the first and second temperatures and the first and second flow rates are selected such that a temperature of the mixed fluids downstream of said mixing length ( 115, 215 ) is obtained, at which said first fluid being substantially non-corrosive.

TECHNICAL FIELD OF THE INVENTION

The present invention generally relates to an apparatus for mitigationof corrosion in a high pressure and high temperature reaction system,specifically in a system suitable for oxidative waste treatment undersupercritical water conditions. The invention relates further to thereaction system itself and to a method in said reaction system.

DESCRIPTION OF RELATED ART AND BACKGROUND OF THE INVENTION

Several approaches for disposing of waste are available today, of whichthe major ones are landfilling and incineration. In recent years,another technique based on supercritical water oxidation (SCWO) has beencommercialized, see, e.g. Supercritical Water Oxidation Aims forWastewater Cleanup, C. M. Caruana, Chem. Eng. Prog., April 1995.

Supercritical water oxidation is a novel and advanced process for, interalia, effective destruction of toxic substances, particularly organicpollutions, in wastewater and sludge. The process converts, fast andeffectively, organic materials containing substantially carbon andhydrogen to carbon dioxide and water, at a temperature above thecritical point of water (374° C. and 22,13 MPa), while releasing energy.The process may be completely contained and the destruction efficiencyis often higher than 99%.

Heavy metals present during the process are converted to their oxideswhereas sulfur and phosphorous are converted to sulfate and phosphate,respectively. Halogens are converted to their corresponding acids, e.g.,hydrochloric acid. Smaller amounts of nitrogen compounds, e.g. aminesand ammonia, which exist in the waste material flow, are converted tomolecular nitrogen, and not to NO_(x), which is an acidifying andfertilizing residual product and therefore undesirable in the effluent.

If, however, the waste material contains large amounts of ammonia and/ororganic nitrogen compounds, substantial amounts of the nitrogen sourcemay be found in the effluent as ammonia as a result of the destructionprocess. This phenomenon is undesirable as ammonia constitutes afertilizing compound. Besides, discharge of ammonia without furtherpurifying is very often imposed with restrictions.

It is known in the literature, e.g. through Reactions of Nitrate Saltswith Ammonia in Supercritical Water, P. C. Dell'Orco et al., Ind. Eng.Chem., Vol. 36, No. 7, 1997, and references therein, that ammonia can beconverted to molecular nitrogen during supercritical water oxidationconditions if nitric acid is used as a co-oxidant together withmolecular oxygen, hydrogen peroxide or another suitable compound. Thenitric acid has preferably to be supplied to the waste material flowfirstly after that the organic contents have been destructed with oxygenas nitrate otherwise will compete with oxygen in the destruction of theorganic contents. Furthermore, the nitric acid has to be dosed with highaccuracy relative to the amount of ammonia (a stoichiometric amount isneeded). If too little nitric acid is supplied, a remaining amount ofammonia will be left whereas too large amounts of nitric acid willresult in an excess of nitrate in the effluent.

For purposes of strength and corrosion, nickel-based alloys, such asHastelloy or Inconel, are employed for manufacturing of equipment forSCWO. Acids, and not at least nitric acid, are, however, in presence ofoxygen strongly corrosive at high temperatures, though still subcriticalones, even if these corrosion resistant nickel alloys are used, see,e.g. The Corrosion of Nickel-base Alloy 625 in Sub- and SupercriticalAqueous Solutions of HNO ₃ in the Presence of Oxygen, P. Kritzer et al.,J. Mater. Sci. Lett., 1999, in print, and references therein. It wasfound in the temperature-resolved corrosion measurements reported thatthe corrosion due to nitric acid was most severe at temperatures betweenabout 270° C. and 380° C., the same temperature range in which generalcorrosion is caused by the mixtures HCl/O₂ and H₂SO₄/O₂, respectively.At supercritical temperatures the corrosion rates were low.

For this reason, particular solutions must be employed for the entry ofnitric acid into the supercritical wastewater flow containing ammonia orammonium salts to avoid or at least minimize the corrosion.

However, as regards corrosion, generally the most troublesome compoundin the supercritical water oxidation process is the chlorine element,since it is very common in various chemical substances. If the chlorineis present as an ion at elevated temperatures, it will corrode theconstruction materials mentioned above. The chlorine may have been anion originally, liberated during heat up or in the reactor.

U.S. Pat. No. 5,358,645 issued to Hong et al. disclose an apparatus andprocess for high temperature water oxidation, the apparatus (not indetail described) having a surface area, that may be exposed tocorrosive material, composed of zirconia based ceramics. The ceramicsmay be employed as coatings or linings.

U.S. Pat. No. 5,461,648 issued to Nauflett et al. disclose asupercritical water oxidation reactor with a corrosion-resistant lining.The inner surface of the reactor vessel is coated with artificialceramic or diamond. A cylindrical baffle for introducing the oxygenatingagent extends axially within the interior of the vessel and has itsexterior surface inside the vessel coated with said artificial ceramicor diamond.

U.S. Pat. No. 5,552,039 issued to McBrayer, Jr. et al. disclose aturbulent flow cold-wall reactor. It mentions, inter alia, that if theatmosphere in the reaction chamber is harsh and corrosive, the insidewall of the reaction chamber should preferably be made of or coveredwith a coating or a liner withstanding the harsh atmosphere.

None of these US patents, is, however, discussing corrosion problems interms of temperature dependent corrosivity, or the particular corrosioncaused by the corrosive compounds discussed above.

SUMMARY OF THE INVENTION

Embodiments of an apparatus and methods for mitigation of corrosion in ahigh pressure and high temperature reaction system that can be used foroxidative waste treatment under supercritical water conditions aredescribed.

In an embodiment of a system and method for oxidative waste treatment, afirst fluid may be transported through a first conduit at a first flowrate and at a first temperature. Construction of the first conduit maybe such that the first conduit may have an end within the interior ofthe second conduit, and is in fluid communication with the secondconduit. Fluid communication between the first conduit and secondconduit may allow the first fluid to be injected into the second fluid.Transportation of the second fluid may occur in a second conduit at asecond temperature and a second flow rate. The first fluid may becorrosive in a corrosive temperature range and the corrosive temperaturerange may exclude the second temperature.

The first and second fluids may be mixed in the second conduit at amixing length downstream of the end of the first conduit. The secondconduit may include a tube or liner having at least an inner surfacearea made of a corrosion resistant material and extending along themixing length to inhibit corrosion of the second conduit. As usedherein, “mixing length” is the distance necessary for a mixed fluid toreach a steady state temperature.

The first and second temperatures and the first and second flow ratesmay be selected such that the mixed fluids downstream of the mixinglength are at a temperature that is substantially non-corrosive for thefirst fluid.

In an embodiment, a high pressure and high temperature reaction systemsuitable for oxidative waste treatment may include a first and a secondconduit adapted to transport a first and a second fluid. The secondconduit may be adapted to transport the second fluid at a secondtemperature and at a second flow rate. Transportation of the first fluidin the first conduit may occur at a first flow rate. The first fluid maybe at a first temperature, which is corrosive in a corrosive temperaturerange, which excludes the second temperature.

The first conduit may have an end within the interior of the secondconduit, which allows the first conduit to be in fluid communicationwith the second conduit. Fluid communication of the first and secondconduits may be such that the first fluid and the second fluid can bemixed in the second conduit within a mixing length from the end of thefirst conduit. As a result of the mixing, the mixed fluids downstream ofthe mixing length may have a temperature substantially non-corrosive forthe first fluid.

The high pressure and high temperature reaction system may have a tubeor liner having at least an inner surface area made of a corrosionresistant material. The tube or liner may be part of the second conduitand may extend along the mixing length to inhibit corrosion of thesecond conduit. The second conduit may be made up of a conventionalconstruction material (e.g., nickel based alloy) upstream and downstreamof the tube or liner configured for high pressure and high temperaturereaction systems suitable for supercritical water oxidation.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description of embodiments of the present invention givenhereinbelow and the accompanying FIGS. 1–3 which are given by way ofillustration only, and thus are not limitative of the invention.

FIG. 1 shows a simplified block diagram of a reaction system suitablefor oxidative waste treatment under supercritical water conditionswherein the present invention may be employed.

FIG. 2 shows, in cross-section, a first embodiment of an apparatusaccording to the present invention.

FIG. 3 shows, in cross-section, a second embodiment of an apparatusaccording to the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

In the following description, for purposes of explanation and notlimitation, specific details are set fourth, such as particularhardware, applications, techniques, etc. in order to provide a thoroughunderstanding of the present invention. However, it will be apparent toone skilled in the art that the present invention may be practiced inother embodiments that depart from these specific details. In otherinstances, detailed descriptions of well-known methods, protocols,apparatus, and circuits are omitted so as not to obscure the descriptionof the present invention with unnecessary details.

Considering FIG. 1, the operation of a high pressure and hightemperature reaction system 10 such as a system suitable for oxidativewaste treatment under supercritical water conditions, will briefly beoverviewed so that in the subsequent detailed description of the presentinvention, the operation of the inventive apparatus may be betterunderstood.

A conventional reaction system 10 comprises a primary tank 12, a heatexchanger 14, a heater 16 and a reaction chamber 18. A primarywastewater stream 20 passes initially through the first compartment (notshown) of the heat exchanger 14, then through the heater 16, and entersthe reaction chamber 18 under pressure, after it has been mixed withoxidant coming through feed line 22. The organic matter contained in theprimary waste stream 20 is oxidized, and in sequence, the hot effluencepasses through the second compartment (not shown) of the heat exchanger14. As well known, heat exchangers usually have two compartments,physically isolated from each other, which, however, areheat-communicating. The second compartment transfers heat to the firstcompartment.

Constructing materials for the reactor and the tubing may comprisesteel, nickel-based alloys, platinum, gold, titanium, zirconium,ceramics, ceramic composites and other corrosion resistant materials asthe environment inside the reaction chamber and tubing may be hostileand corrosive. However, as many of the latter materials are highlyexpensive, an optimal compromise between cost, on one hand, andcorrosion resistance, on the other hand, is to use nickel based alloyssuch as Hastelloy or Inconel, for the manufacturing of such equipment.

As already discussed in the prior art, there is a number of species thatare very aggressive relative to these nickel based alloys within afinite temperature range, among them nitric acid, sulfuric acid andhydrochloric acid. All these three acids are strongly corrosive betweenabout 270 and 380° C., but the corrosion rates for the latter two acidsare lower by a factor of ten than the one found for nitric acid, seesaid Kritzer article.

It is clear from the description above of the operation of the systemthat the wastewater flow, as well as any additives, will be heated frominitial low temperatures, which probably are close to ambienttemperatures, up to supercritical temperatures (above 374° C.) for theoxidative treatment of the waste, whereafter the effluent is cooledeither in a heat exchanger or by mixing it with quench water or acombination of both.

The present inventors have realized that if the initial temperatures andthe temperature of the cooled effluent are kept preferably well below270° C. and the temperature in the reaction chamber is kept preferablyabove 380° C., there is generally only two sections of a reaction systemmade of nickel-based alloy that may be attacked by corrosive agents suchas those mentioned above contained in, or supplied to, the wastewaterflow, namely a “heating” section and a “cooling” section, where thetemperatures are within the temperature interval of said corrosion.

The present invention is thus concerned with such sections of thereaction system and how to design them in order to provide a reactionsystem of low cost and good corrosion resistance. The idea is to provideappropriate tubing (made of nickel based alloy or other, preferablyrelatively inexpensive, material that is not corrosive resistant) of thesystem with a corrosive resistant tube or liner. The number of tubes orliners, their positions and their lengths are chosen in order to protectthe system from corroding.

Hereinbelow will follow a few implementation examples of the presentinvention. Note that the terms “corrosive” and “corrosive-resistantmaterial” as used in the description below and in the appended claimsshould be understood as “corrosive” relative conventional constructionmaterial for high pressure and high temperature reaction systemssuitable for supercritical water oxidation such as steel, nickel basedalloys, nickel-chromium alloys and the like, at least within a giventemperature interval, and “corrosive-resistant material” refers tounconventional expensive material which is corrosion-resistant relativea wide variety of harsh media such as acids, particularly the acidsdiscussed above, halogens and the like, respectively. Examples ofcorrosion-resistant materials will be given below.

A first embodiment of the present invention, shown in FIG. 2, depicts anapparatus 101 for introducing nitric acid in a supercritical water flowcontaining ammonia or ammonium with the purpose of converting this tomolecular nitrogen.

In a section of a reaction system tube 103, which preferably is theconduit between the heater 16 and the reaction chamber 18, or part ofthe reaction chamber itself, of FIG. 1, a separate tube or liner 105 ofa corrosion resistant material is mounted, the outer surface of which isin fit with the inner surface of reaction system tube 103.Alternatively, tube 105 constitutes part of the reaction system tube 103itself (not shown).

A feeding pipe 107 of relatively small diameter, is mounted through anopening of tube 103 and extends substantially axially with tube 103 andliner 105, and which ends in the interior of tube 103. Preferably,feeding pipe 107 and tube 103 are concentrically arranged fortransportation of fluids, the former nitric acid and the latterpreheated wastewater feed, in the same directions, as indicated byarrows 109–113. The temperature of the wastewater should preferably beabove 380° C., and the temperature of the nitric acid should be low,preferably considerably lower than 270° C. Note that if theconcentration of the corrosive agent is low, these temperature limitsare not very crucial, i.e., the corrosion would be low at temperaturesslightly lower than 380° C. and, particularly, at temperatures slightlyhigher than 270° C., e.g., 300° C.

By pumping nitric acid through the feeding pipe it will be preheated bythe hot water flow and then get mixed with the supercritical water. Theflow rates are such that the total flow (wastewater and nitric acid)becomes supercritical with a temperature of above 380° C. after havingreached a steady temperature state a certain distance 115 from the endof the feeding pipe, said distance being referred to as the heattransfer or mixing length. Accordingly, to avoid any risk of corrosionof the inner walls of tube 103, the length of the liner 105 should be ofat least this length, and it should be localized to protect the innerwalls of tube 103 within this length. For practical reasons, the liner105 may have an offset 117 in the end facing the end of the feedingpipe, i.e. extend beyond (upstream of) said feeding pipe end to avoidany risk of corrosion in that region.

The material of the liner and preferably of the feeding pipe is chosenaccording to its corrosion resistance relative nitric acid at theoccurring temperatures. Literature data shows that titanium, generally,is a suitable material, but also materials such as zirconium, platinum,tantalum, niobium and ceramics may be chosen. The entire liner, or aninner coating thereof, may be constructed of such material.

Even if a limited degree of corrosion may exist using these materials,the components are relatively cheap and easy to replace when so needed.

Preferably, there are means for positioning and/or holding the liner inplace. In the embodiment showed, tube 103 is provided with an elbow atthe downstream end of the mixing length to prevent liner 105 from movingfurther downstream. However, any suitable means for positioning and/orholding the liner, e.g. flanges at the inner walls of tube 103, may beused.

In experimental work, an injection apparatus as the one shown in FIG. 2,was used, the liner and the feeding pipe being made of titanium. Theammonia destruction was performed by pumping 65% nitric acid into thereaction system during several hours without any detected corrosion.When the liner and the feeding pipe were demounted and inspected nocorrosion of these components was discovered. In contrast thereto, in anexperiment in which nitric acid was pumped into a supercritical waterflow containing ammonia through a T-pipe of Inconel 625, the pipe wasdestroyed through corrosion in just a few hours.

Consequently, by using an injection apparatus according to FIG. 2,nitric acid may safely be introduced without severe corrosion of thereaction system.

Furthermore, a substantial portion of the reaction between nitric acidand ammonia and/or ammonium will take part as early as in the section ofthe reaction system where the liner is localized, which further reducesthe risk for severe corrosion.

Alternatively, feeding pipe 107 and tube 103 of FIG. 2 may be arrangedfor transportation of a wastewater feed containing a corrosive agentsuch as a halogen, and water or a wastewater feed in lack of such acorrosive agent, respectively. The water or wastewater in tube 103 ispreferably at a supercritical temperature, whereas the corrosivewastewater may be cooler.

Referring next to FIG. 3, which illustrates an apparatus 201 accordingto a second embodiment of the present invention, a separate tube orliner 205 of a corrosion resistant material is mounted in a section of areaction system tube 203, which is preferably at the effluent output orelsewhere in the exit path tubing. The outer surface of liner 205 isarranged to be in fit with the inner surface of the reaction system tube203.

A first input tube 207, is mounted through an opening of tube 203 andextends substantially axially, preferably concentrically, with tube 203and liner 205, and which ends in the interior of tube 203. A secondinput tube 208 is connected to tube 203 upstream from said end of inputtube 207.

Input tube 207 and input tube 208 are arranged for transporting effluentfrom reactor 18 containing corrosive compounds such as nitric acid,sulfur acid, or the like, and quench water, respectively, in thedirections as indicated by arrows 209–213. The effluent stream issupercritical or close to supercritical, and the temperature of thequench water is low, preferably at ambient temperature.

By pumping appropriate amounts of quench water through input tube 208,the effluent input through tube 207 will be cooled effectively by thequench water and get mixed with it. The flow rates are such that thetotal flow (effluent and quench water) will have a temperature of belowa certain temperature, e.g. 270° C., depending on concentration ofcorrosive compounds, after having reached a steady temperature state acertain distance 215 from the end of the input tube 207, said distancebeing referred to as the mixing length. Accordingly, to avoid any riskof corrosion of the inner walls of tube 203, the length of the liner 205should be at least of this mixing length, and it should be localized toprotect the inner walls of tube 203 within this length. For practicalreasons, the liner 205 may have an offset 217 in the end facing the endof tube 207, i.e. extend beyond (upstream of) said tube end, to avoidany risk of corrosion in that region.

The material of the liner and preferably of tube 207, as well assuitable means for positioning and/or holding the liner in place may bechosen as in the first embodiment.

The first and the second embodiments of the present invention may bemodified to include a heat exchange for assisting in increasing ordecreasing the temperature in tubes 103 and 203, respectively. Hereby,the lengths of liners 105 and 205, respectively, may be shortened.

As a further example of an implementation of the present invention (notillustrated in the drawings), an effluent from the reactor containingchlorine ions is pre-cooled in a heat exchanger by part of the incomingwaste stream, to a temperature well above 380° C., e.g., 400° C. Theeffluent is then cooled by an apparatus according to the presentinvention to a sufficient low temperature, e.g., 260° C., to minimizecorrosion. After leaving the apparatus, the effluent water mixture isfurther cooled by the remaining of the waste stream.

It will be obvious that the invention may be varied in a plurality ofways. For instance, the geometry and function of the reaction system andthe appearance of the tubing may deviate substantially from thedescription above. Such and other variations are not to be regarded as adeparture from the scope of the invention. All such modifications aswould be obvious to one skilled in the art are intended to be includedwithin the scope of the appended claims.

1. A method for injecting a first fluid of a first temperature at afirst flow rate into a second fluid of a second temperature at a secondflow rate in a high pressure and high temperature reaction systemsuitable for oxidative waste treatment, comprising: transporting thefirst fluid in a first conduit adapted to transport the first fluid;transporting the second fluid in a second conduit adapted to transportthe second fluid, wherein the first conduit comprises an end within theinterior of the second conduit, and wherein the first conduit is influid communication with the second conduit; mixing the first and thesecond fluids in the second conduit within a mixing length downstream ofthe end of the first conduit, wherein the second conduit comprises atube or liner having at least an inner surface area made of a corrosionresistant material and extending along the mixing length to inhibitcorrosion of the second conduit; wherein the first fluid is corrosive ina corrosive temperature range; wherein the corrosive temperature rangeexcludes the second temperature and includes the first temperature;wherein the second temperature is selected to be lower than thecorrosive temperature range; wherein the first and second temperaturesand the first and second flow rates are selected such that thetemperature of the mixed fluids downstream of the mixing length is lowerthan the corrosive temperature range; and wherein the first and secondtemperatures and the first and second flow rates are selected such thatthe mixed fluids downstream of the mixing length are at a temperaturethat is substantially non-corrosive for the first fluid.
 2. The methodof claim 1, wherein the first fluid is corrosive at the firsttemperature, and wherein at least an inner surface area of the firstconduit is made of a corrosion resistant material to inhibit corrosionof the first conduit.
 3. The method of claim 1, wherein the first fluidcomprises nitric acid, and wherein the corrosive temperature range isbetween about 270° C. and about 380° C.
 4. The method of claim 1,wherein the first fluid comprises sulfuric acid.
 5. The method of claim1, wherein the first fluid comprises hydrochloric acid.
 6. The method ofclaim 1, wherein the first fluid comprises a halogen.
 7. The method ofclaim 1, further comprising feeding the mixed fluids from the secondconduit to a reactor of a high pressure and high temperature reactionsystem for oxidation of waste material.
 8. The method of claim 1,wherein the second conduit comprises part of a reactor of a highpressure and high temperature reaction system for oxidation of wastematerial.
 9. The method of claim 1, wherein the second fluid comprisescooling water.
 10. The method of claim 9, wherein the first fluidcomprises destructed supercritical wastewater output from a reactor of ahigh pressure and high temperature reaction system.
 11. The method ofclaim 10, wherein the mixed fluids in the second conduit are output fromthe high pressure and high temperature reaction system.
 12. The methodof claim 1, wherein at least the inner surface area of the tube or lineris made of a material selected from the group consisting of titanium,zirconium, platinum, tantalum, niobium, or alloys thereof.
 13. A methodfor injecting a first fluid of a first temperature at a first flow rateinto a second fluid of a second temperature at a second flow rate in ahigh pressure and high temperature reaction system suitable foroxidative waste treatment, comprising: transporting the first fluid in afirst conduit adapted to transport the first fluid; transporting thesecond fluid in a second conduit adapted to transport the second fluid,wherein the first conduit comprises an end within the interior of thesecond conduit, and wherein the first conduit is in fluid communicationwith the second conduit; mixing the first and the second fluids in thesecond conduit within a mixing length downstream of the end of the firstconduit, wherein the second conduit comprises a tube or liner having atleast an inner surface area made of a corrosion resistant material andextending along the mixing length to inhibit corrosion of the secondconduit; wherein the first fluid is corrosive in a corrosive temperaturerange; wherein the corrosive temperature range lies between the firsttemperature and the second temperature; wherein the second temperatureis selected to be lower than the corrosive temperature range; whereinthe first and second temperatures and the first and second flow ratesare selected such that the temperature of the mixed fluids downstream ofthe mixing length is lower than the corrosive temperature range; andwherein the first and second temperatures and the first and second flowrates are selected such that the mixed fluids downstream of the mixinglength are at a temperature that is substantially non-corrosive for thefirst fluid.
 14. The method of claim 13, wherein the first fluidcomprises sulfuric acid.
 15. The method of claim 13, wherein the firstfluid comprises hydrochloric acid.
 16. The method of claim 13, whereinthe second fluid comprises cooling water.
 17. The method of claim 16,wherein the first fluid comprises destructed supercritical wastewateroutput from a reactor of a high pressure and high temperature reactionsystem.
 18. The method of claim 17, wherein the mixed fluids in thesecond conduit are output from the high pressure and high temperaturereaction system.
 19. The method of claim 13, wherein the first fluidcomprises nitric acid, and wherein the corrosive temperature range isbetween about 270° C. and about 380° C.
 20. A method for injecting afirst fluid of a first temperature at a first flow rate into a secondfluid of a second temperature at a second flow rate in a high pressureand high temperature reaction system suitable for oxidative wastetreatment, comprising: transporting the first fluid in a first conduitadapted to transport the first fluid; transporting the second fluid in asecond conduit adapted to transport the second fluid, wherein the firstconduit comprises an end within the interior of the second conduit, andwherein the first conduit is in fluid communication with the secondconduit; mixing the first and the second fluids in the second conduitwithin a mixing length downstream of the end of the first conduit,wherein the second conduit comprises a tube or liner having at least aninner surface area made of a corrosion resistant material and extendingalong the mixing length to inhibit corrosion of the second conduit, andupstream and downstream of the tube or liner, the second conduitcomprises a construction material for high pressure and high temperaturereaction systems suitable for supercritical water oxidation; wherein thefirst fluid is corrosive in a corrosive temperature range; wherein thecorrosive temperature range excludes the second temperature and includesthe first temperature; wherein the second temperature is selected to behigher than the corrosive temperature range; wherein the first andsecond temperatures and the first and second flow rates are selectedsuch that the temperature of the mixed fluids downstream of the mixinglength is higher than the corrosive temperature range; and wherein thefirst and second temperatures and the first and second flow rates areselected such that the mixed fluids downstream of the mixing length areat a temperature that is substantially non-corrosive for the firstfluid.
 21. The method of claim 20, wherein the first fluid comprises ahalogen.
 22. The method of claim 20, wherein the second fluid comprisessupercritical water.
 23. The method of claim 22, wherein the secondfluid comprises nitrogenous compounds.
 24. The method of claim 20,wherein at least the inner surface area of the tube or liner is made ofa material selected from the group consisting of titanium, zirconium,platinum, tantalum, niobium, or alloys thereof.
 25. The method of claim20, wherein the first fluid comprises nitric acid, and wherein thecorrosive temperature range is between about 270° C. and about 380° C.26. The method of claim 20, wherein the first fluid comprises sulfuricacid.
 27. The method of claim 20, wherein the first fluid compriseshydrochloric acid.
 28. A method for injecting a first fluid of a firsttemperature at a first flow rate into a second fluid of a secondtemperature at a second flow rate in a high pressure and hightemperature reaction system suitable for oxidative waste treatment,comprising: transporting the first fluid in a first conduit adapted totransport the first fluid; transporting the second fluid in a secondconduit adapted to transport the second fluid, wherein the first conduitcomprises an end within the interior of the second conduit, and whereinthe first conduit is in fluid communication with the second conduit;mixing the first and the second fluids in the second conduit within amixing length downstream of the end of the first conduit, wherein thesecond conduit comprises a tube or liner having at least an innersurface area made of a corrosion resistant material and extending alongthe mixing length to inhibit corrosion of the second conduit andupstream and downstream of the tube or liner, the second conduitcomprises a construction material for high pressure and high temperaturereaction systems suitable for supercritical water oxidation; wherein thefirst fluid is corrosive in a corrosive temperature range; wherein thecorrosive temperature range lies between the first temperature and thesecond temperature; wherein the second temperature is selected to behigher than the corrosive temperature range; wherein the first andsecond temperatures and the first and second flow rates are selectedsuch that the temperature of the mixed fluids downstream of the mixinglength is higher than the corrosive temperature range; and wherein thefirst and second temperatures and the first and second flow rates areselected such that the mixed fluids downstream of the mixing length areat a temperature that is substantially non-corrosive for the firstfluid.
 29. The method of claim 28, wherein the first fluid comprises ahalogen.
 30. The method of claim 28, wherein the second fluid comprisessupercritical water.
 31. The method of claim 30, wherein the secondfluid comprises nitrogenous compounds.
 32. The method of claim 28,wherein at least the inner surface area of the tube or liner is made ofa material selected from the group consisting of titanium, zirconium,platinum, tantalum, niobium, or alloys thereof.
 33. The method of claim28, wherein the first fluid comprises sulfuric acid.
 34. The method ofclaim 28, wherein the first fluid comprises hydrochloric acid.
 35. Themethod of claim 28, wherein the first fluid comprises nitric acid, andwherein the corrosive temperature range is between about 270° C. andabout 380° C.